Many surgeries (e.g., spinal and orthopedic surgeries) currently require the use of medical images displayed to the surgeon in real time, to provide visual navigation to support surgical action, gestures, and decision making. Using medical images, a surgeon can be provided with real-time feedback of the position of surgical instruments in reference to patient anatomy (as pictured by medical images).
Current surgical navigation systems are based on the principle of tracking. For example, a navigation system generally contains a tracking device which measures position of the surgical instruments and patient in real time. Different tracking devices operate on different principles. The most popular are optical tracking and electro-magnetic tracking. Optical tracking uses camera systems that measure fiducials (e.g., reflective spheres, LEDs) configured on markers having defined and known anatomy. In this way, the position and orientation of a marker can be determined and, thus, the position and orientation of the element to which they are affixed (e.g., surgical instruments, patient anatomy) can be tracked as well. In electro-magnetic tracking, the camera of an optical tracking system is replaced by a field generator. Markers are sensor units (e.g., coils) which measure spatial changes in the generated field. In this way, the position and orientation of the EM marker can be determined in reference to field generator.
There are commercial navigation systems available on the market, for example, Stealthstation S7 from Medtronic, Curve from Brainlab, electro-magnetic Kick EM from Brainlab and others. A typical workflow for use of these navigation systems follows the steps of: obtaining patient images, fixing a reference on the patient, registering the patient, and tracking instrument and patients to show real-time feedback to the surgeon. Patient images may be generated by CT, MRI, or flat-panel fluoroscopy (e.g., O-Arm), for example. References fixed to the patient include optical markers with a fiducial mark or electro-magnetic markers. Markers are fixed using, for example, bone screws or bone fixations. Registering the patient requires defining a relationship between the patient images and the fixed marker. Registration may be performed using a point-to-point method, surface matching, or automatic registration based on images taken with fixed markers (e.g., on the patient's anatomy).
Current navigation systems have numerous limitations. These navigation systems are generally difficult to use and require additional surgeon and/or staff training for their operation. The navigation systems take up a lot of space in the operating room. For example, precious real estate in the operating room space may be occupied by a stand-alone navigation station/console with tracking camera, screens used for visual feedback, cords and plugs, power systems, controllers, and the like, creating additional clutter. Also, current optical navigation systems have a line of sight requirement, in that all tracked instruments must remain visible to the camera in order to be tracked. If there are not enough fiducials (e.g., spheres, LEDs) visible marker positions may not be able to be determined. An additional risk is that fiducial position can be misread by the navigation system due to obfuscation (e.g., by a drop of blood or transparent drape). Electro-magnetic navigation systems have problems with metal and ferromagnetic materials placed in field which can influence the field and thus add error to marker position measurement. Moreover, navigation systems are expensive, costing approximately $200 k or more. The precision of the measurement is relatively low in commercial stations, for example, on the level of 0.3 mm RMS error for position measurement. Additionally, the measurements are noisy. The frequency of measurement is low (i.e., approximately 20 Hz).
The most severe limitation of known navigation systems is that the navigation desynchronizes over time. The surgeon registers the patient initially at the beginning of the surgical procedure, using one or more markers attached to the patient's anatomy. Throughout the surgical procedure, the patient's anatomy shifts due to movement of the patient or as a result of the surgical procedure itself. For example, in surgeries involving elongation steps or realignment steps, the patient's anatomy will have a different position and orientation relative to the fiducial marker(s) after the elongation or realignment. Only the area local to the fiducial marker(s) remains accurate to the physical reality of the patient's anatomy. The error between the reality of the patient's anatomy and the assumed reality based on the initial registration increases with distance from the fiducial marker(s). Thus, in many surgical procedures being performed today using robotic surgical systems with known navigation systems, as the procedure progresses, the navigation system becomes more desynchronized and thus less useful to the surgeon, as it is less reflective of real life. Likewise, the likelihood of complications and serious medical error increases.
There are robotic surgical systems which are combined with a navigation system, for example, Excelsius GPS from Globus, ROSA SPINE from Medtech (currently Zimmer/Biomet), MAKO from Stryker and others. However, these systems use the same navigation system approach as the aforementioned known systems. The use of a robotic arm aids a surgeon in making precise gestures, but the systems inherit the disadvantages of navigation systems especially: training requirements, required space, line of sight, price and low precision of optical navigation over the course of a surgical procedure. The likelihood of complications and serious medical errors due to desynchronization are not reduced in these robotic surgical systems.
Thus, there is a need for robotic surgical systems for instrument guidance and navigation wherein the patient registration can be updated overtime to accurately reflect the instant patient situation.